Mechanical Mechanism Analysis of Warping and Bulging Of Track Slab of High-Speed Railway in Service

Due to warpage and ballooning of high-speed rail track slab caused by debonding and environmental temperature changes during the deterioration of CA mortar layer being extremely concerned in practical engineering, it is based on numerical simulation of typical working conditions and analysis of test model that the deformation dynamics mechanism of track slab of high-speed rail in service is studied in this paper. Firstly, three kinds of damage conditions of CA mortar layer are designed to simulate the partial stress state of track slab under normal, warping and bulging conditions, and the results of model test are compared with those of finite element analysis so that the accuracy and credibility of the numerical simulation method and results are verified. Then, through finite element numerical simulation, the dynamical mechanism of actual full-scale high-speed rail track slab under vibration load is studied. The results show that the warping deformation around the track slab and the bulging deformation in the middle part under the action of positive and negative temperature gradient load caused by environmental temperature change will have a great impact on the structural performance of itself and CA mortar layer; Bulging deformation of track slab is more destructive to its structure than warping deformation. It is of great practical significance to further study the critical position of track plate warpage and bulging deformation, and to optimize and strengthen the structure of this part; The research results are of great significance to further study the deterioration.

A Review on Cement Asphalt Emulsion Mortar Composites, Structural Development, and Performances

The use of cement emulsified asphalt mortar (CA mortar) in the track structure of high-speed speed railways has been gaining considerations by many researchers due to its coupled merits of the strength of cement as well as the flexibility of asphalt material. The asphalt to cement ratio (A/C) and the compatibility among constituent materials are crucial to the properties of CA mortar. To improve the performance properties and application of CA mortar, it is imperative to have a broad understanding of the composition mechanisms and compatibility between constituent materials. This paper summarizes interesting research outcomes related to the composition and properties of CA mortar. The consumption of water by cement promotes the breakdown of emulsified asphalt, likewise, the adsorption of asphalt droplets on the surface of cement grains retards the hydration process of cement. An appropriate A/C is required for the cement hydration rate to match the speed of demulsification of asphalt emulsion. Depending on the type and properties for which the CA mortar is designed to possess, the A/C ranges from 0.2 to 0.6 for type 1 (CAM I), and 0.6 to 1.2 for type 2 (CAM II). This paper also discusses measures taken to improve performance properties, compatibility, the interaction between constituent materials of CA mortar, and the use of additives as a partial replacement of cement in CA mortar production. The current review also suggests areas of interest for future research studies. This paper is useful to those who aim to understand or study the composition mechanisms and performance properties of CA mortar.

Early Hardening Process of CA Mortar Indicated by Electrical Resistivity

A non-contact electrical resistivity measurement device was employed to indicate the early hardening process of cement asphalt emulsified mortar (CA mortar). It was found that this process was analogous with the hydration process of cement and could be categorized into three parts: dissolving period, induction period and setting period. The mortar resistivity first decreased and then increased with the elapsed time. The effect of water/cement ratio (W/C), asphalt emulsified/cement ratio (A/C), cement types were also explored. Results indicated that the increase of W/C, dosages in SF (Silica fume) extended the induction period; replacement of Portland cementII with sulfoaluminate cement in CA mortar markedly increased the electrical resistivity and advanced the onset of setting period by 5∼6 h, making it possible to prepare CA mortar with high early strength, which can preventing distress such as peeling and bleeding during construction in winter and conformance to requirements in acceptance standard.

Preliminary Study on Assessing Delaminated Cracks in Cement Asphalt Mortar Layer of High-Speed Rail Track Using Traditional and Normalized Impact–Echo Methods

The severe deterioration of a cement asphalt (CA) mortar layer may lead to the movement of the upper concrete slab and impair the safety of the speedy train. In this study, a test specimen simulating the structure of high-speed rail track slabs was embedded with delaminated cracks in various lateral sizes inside the CA mortar layer. Impact–echo tests (IE) were performed above the flawed and flawless locations. In present study, the IE method is chosen to assess defects in the CA mortar layer. Both traditional IE and normalized IE are used for data interpolation. The normalized IE are the simulated transfer function of the original IE response. The peak amplitudes in the normalized amplitude spectrum and the peak frequency in the traditional amplitude spectrum for the top concrete overlay were used to develop simple indicators for identifying the integrity of the CA mortar layer. The index was based on the difference of the experimental peak amplitude and frequency of the ones calculated from previously developed formulas for plates without substrates. As a result, the technique does not require an experimental baseline for the crack assessment. A field test and analysis procedure for evaluating high-speed rail slab systems are proposed.

Experimental Investigation of Stochastic Mechanical Behavior of Cement Emulsified Asphalt Mortar under Monotonic Compression

Experimental investigation on cement emulsified asphalt mortar (CA mortar) under uniaxial monotonic compression by taking into account the stochastic properties were investigated. An analytical constitutive model based on the statistic damage approach capable of mimicking the stochastic mechanical responses of CA mortar under uniaxial compression was proposed. The comparison between the experimental results and the predictions demonstrated that the proposed model was able to characterize the salient features for CA mortar under uniaxial monotonic compression. Furthermore, the compressive stochastic evolution (SE) of CA mortar tested in this work and comparative analyses among typical China Railway Track System-I (CRTS-I) type CA mortar and concrete in several aspects were examined and performed; it was revealed that the Lognormal distribution density function can well represent the damage probability density for CA mortar, and its stochastic constitutive relationship can be reflected by a media process of transition from microscale to macroscale.